The overall aim of the proposed research is that of better defining the roles of calcium ion and cAMP as intracellular messengers in the actions of hormones and neurotransmitters. The specific problems to be investigated are: 1) the isolation and identification of calcium binding proteins in the cell cytosol, other than calmodulin, which may serve a calcium buffering function; 2) the mechanism by which cAMP regulates calcium exchange in intact cells and isolated mitochondria; 3) elucidate the mechanism by which the peptide hormone, angiotensin II regulates calcium influx in isolated adrenal glomerulosa cells and define the intracellular sites of calcium action; 4) determine the effects of ACTH upon glomerulosa cell calcium metabolism and compare them with the effects of angiotensin; 5) define the mechanism by which cholera toxin alters Na plus-dependent glucose transport in isolated membrane vesicles from the intestinal brush border; and 6) determine the molecular basis for the potentiating effect of cAMP on the calcium-regulated contraction of buccal muscle in Aplysia.